INDIANAPOLIS, Ind. — A terrific debate arose at the Commercial Vehicle Safety Alliance Brake Safety Symposium (CVSA) in Indianapolis not too long ago, between three manufacturers of air disc brakes and several CVSA inspectors on how to inspect these brakes at roadside.

The trucking industry is awaiting a final rule by the U.S. National Highway Traffic Safety Administration (NHTSA), which is proposing a stopping-distance reduction of 20-30 percent for three-axle highway tractors. That means major market penetration for air disc brakes.

Led by Lt. Charles Hanafin, training coordinator for commercial vehicle enforcement with the Massachusetts State Police, the inspectors wanted to know how to determine if and when an air disc brake could be declared out of service.

Highway inspectors insist they need better ways
to tell if disc brakes are in satisfactory condition

But they don’t have external adjustment mechanisms like S-cam brakes. Given that all of the working parts on an air disc brake are inside the caliper, an external visual inspection won’t reveal much.

The brake people, led by Paul Johnston of ArvinMeritor, countered that air discs really can’t go out of adjustment.

“They’re subject to normal wear,” Johnston told the crowd, “but there’s really very little that could go wrong with any of these systems.”

He explained that on each of the three different air disc brands, there are ways to determine if the internal components are working properly, though each is slightly different. He told the inspectors that with air discs, as the brake heats up during normal use, the rotors will expand, tightening the clearance between the rotor and the pad.

That means an air disc actually performs better as it heats up, while the opposite is the case with S-cam brakes.

Still, the inspectors remained skeptical. “We need to be able to tell if the brake is in satisfactory condition to be operating on our highways,” said Hanafin. “We know drivers don’t do proper brake inspections, so there has to be some way of determining if these things are working properly.”

Hanafin then urged the three brake manufacturers to explore ways of developing some sort of an external indicator that drivers, technicians and inspectors might rely on to prove the air disc brakes are up to snuff.

Johnston and his counterparts at Bendix Spicer and Haldex, Ron Planton and Randy Petresh respectively, agreed to look into the issue.

— For more on the stopping distance rule and air disc brake technology info be sure to check out our Braking Systems (link below) section in our exclusive Decision Centers, only on TodaysTrucking.com.